Polynorbornene is a commercially available polymer having the following structural formula: ##STR1## which is available from American Cyanamid Company under the trademark, NORSOREX.RTM.. Polynorbornene is known to be formed from norbornene monomer by use of trace amounts of a ruthenium chloride catalysts as is shown in U.S. Pat. No. 3,676,390. Polynorbornene is available commercially as a free-flowing powder which readily absorbs high levels of oils and fillers and is converted into an elastomer. The end product can be tailored into many various items having desirable properties of permeability, compression set, tensile strength, elongation, and hardness. Details are described in a series of technical reports published by American Cyanamid in 1977 and 1978, all of which are available from the American Cyanamid Corporation.
There currently exists a need for easily fabricated solid combustible materials which either may or may not be self-sustaining. With respect to the nonself-sustaining items, they are used in solid fuel ramjet, or hybrid rocket motors, for example, which are presently under consideration for high speed, high altitude targets and missile systems. In the solid fuel ramjet and hybrid rocket systems the solid fuel material is contained within a combustion chamber and is caused to burn by reaction with either inducted air or an on-board oxidizing agent such as fuming nitric acid, oxygen or halogen, for example, or various combinations of the above. In these applications, the solid fuel material is not capable of self-sustained combustion but must be in a form which is capable of being readily ignitable and capable of burning cleanly and completely with the release of large amounts of energy and also have the necessary physical and structural properties to withstand the rather extreme environments of heat, cold, and acceleration.
Solid propellants and ducted rocket gas generators have basically the same general requirements, but in these situations the fuel material contains sufficient solid particulate oxidizing agents so that it is capable of self-sustained combustion and is independent of any external or auxiliary source of oxidizer for its combustion. The gas generating compositions differ primarily in the amount of oxidizer, solid propellants producing a highly oxidized exhaust gas whereas ducted rocket gas generators produce a fuel-rich exhaust which is subsequently burned with air in the propulsion combustion chambers. For convenience, solid propellants and gas generator grains will be referred generally as "solid gas generating compositions." They are both self-sustaining and differ primarily in the amount of oxidizer they contain.
Typical of the current state-of-the-art, nonself-sustaining combustible materials are fuel grains made from polymethylmethacrylate and various rubbery polymers such as carboxy and hydroxy terminated polybutadienes, polybutadiene-acrylonitrile polymers (PBAN) and polystyrene-polybutadiene polymers, for example.
Composite solid propellants, as opposed to double base solid propellants, are also formed from similar rubbery polymers having solid particulate oxidizer and other conmbustion modifying agents dispersed throughout the mass. With respect to solid propellants, the more advanced propellants utilize hydroxy terminated polybutadiene polymers because they are capable of achieving a higher solids loading than the PBAN or carboxy terminated polymeric materials. However, the pot-life of the hydroxy-terminated polymers is substantially shorter than that of the other types of polymers, and processing problems arise in mixing and casting of the solid propellant grains. With respect to the non-staining compositions, the energy obtained is adequate but none of the previously developed solid fuel compositions are capable of achieving the energies which result with the use of the more advanced liquid ramjet fuels noted above.
Summarizing, most of the presently available liquid elastomers now in use for making solid fuel for ramjets, and hybrid rocket motors, and for making composite solid propellants suffer from several common disadvantages. They permit only limited oil extension, they require expensive and toxic curatives (di-isocyanates, polyaziridines, polyepoxides) which must be used in carefully controlled concentrations, they cure very slowly (many hours or days at 60.degree. to 75.degree. C.), and the rate of cure is subject to catalysis by trace impurities. Fabrication of solid fuel ramjet grains from conventional solid elastomers, or on the other hand, requires the use of expensive high energy Banbury mixers or mills and high pressure hydraulic molding equipment. Further, the available solid ramjet fuels have heats of combustion lower than desired. For example, an advanced solid ramjet fuel known as UTX8818 has a heat of combustion of 9320 Kcal/cc, and the military has needs for solid ramjet fuels with higher heats of combustion.
According to this invention, solid combustible material grains may be fabricated by taking advantage of the polynorbornene's availability in the form of a porous powder which can produce strong highly extensible rubbers which can also be vulcanized. In practice the polynorbornene would be introduced into a suitable mold which may or may not have a mandrel contained therein for making complex star grains or multiport grains, for example. The solid polynorbornene may also be admixed with fuel or propellant ingredients such as solid oxidizers, silica, carbon black, aluminum powder, combustion catalysts, antioxidants, metal deactivators, polystyrene beads, cyclopentadiene resins, Binor-S, decacyclene, etc.) and thereafter charged into the mold. The liquid fuel or plasticizer materials which may also contain a suitable peroxide or sulfur-based vulcanizing agent is then added to the mold and mixture allowed to set.
According to this invention, we have found that when polynorbornene is used as the binder material, a rubbery polymeric fuel material having extremely desirable physical and chemical properties can be obtained which has dispersed therethrough or dissolved therein significantly large quantities of liquid fuel materials. Polynorbornene may also be used as the binder for solid particulate oxidizing agents as well as various other fuels, plasticizers, reinforcing agents such as carbon black and metal powders, tackifiers and combustion modifying materials such as burning rate catalysts and antioxidants all as is known to the art. These compositions can be tailored to be readily ignitable, to burn with the desired clean combustion characteristics at high heats of combustion, and to have desirable physical properties of elongation, strength, and toughness. In addition, the polynorbornene materials bond well to conventional motor insulation materials and can be readily fabricated by casting or molding techniques into the desired configuration for fuel and propellant grains. In the processing area, particularly with respect to the use of self-sustaining gas generating compositions, the problems inherent in the pot-life of conventional materials are overcome by the readily controllable and longer pot-life of the polynorbornene compositions. In addition, by appropriate techniques the combustible compositions of this invention can be formed directly from the monomer by polymerization of the monomer in admixture with the various other compositions described herein.
It is accordingly an object of this invention to provide combustible compositions comprising polynorbornene containing large amounts of liquid fuel materials having heats of combustion above about 9300 Kcal/cc.
It is another object of this invention to provide novel compositions of polynorbornene and solid particulate oxidizing agents.
It is another object of this invention to provide novel methods of fabrication of solid polynorbornene-based combustible materials. It is a further object of this invention to provide novel solid fuel and solid, self-sustaining gas generating compositions based on polynorbornene as a binder. It is another object of this invention to provide novel methods and apparatus for burning polynorbornene base polymeric compositions to produce combustion gases or propulsive force.